Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Doppler Effects and other sources of discrepancy between the time-scale of emission and the time-scale of reception play a significant role in many communication and other signal transmission systems. In Broadband communication cases, a received signal is typically distorted because of Doppler effects, which induce a change in the relative time-scale between the signal emission process and the signal reception process. As such, a significant challenge in underwater acoustic (UWA) communications is the proper compensation for time-scale differences between the emission signal at the transmitter and the received signal at the receiver. These time-scale differences occur due to motion of either the source or receiver, changes in the motion or velocity of the medium of propagation, or even due to electronic means, such as asynchrony in the timing references used in the source and receiver.
Further, due to its large delay spread and rapid time variation, a UWA channel is particularly challenging for high-data-rate digital communications. The transmitted signal bandwidth can be also a substantial fraction of its center frequency making the common narrowband assumptions invalid. Broadband transmissions as in UWA communications can experience highly time-varying Doppler. However, conventional approaches to Doppler compensation often assume a constant velocity difference between the source and receiver, or equivalently, a constant time-scale factor between the source and receiver processes. Conventional approaches estimate an average or bulk Doppler factor directly from the received waveform. For compensation, the received baseband signal is then resampled and phase corrected based on this factor and a phase-locked loop is employed to remove any residual Doppler. This approach is prone to instabilities, since an estimation error in the Doppler Effect may be increasingly amplified with time.
Therefore, there is a need for a system and method that address and overcome the above discussed disadvantages and limitations.